Day-care owner Erica Diaz, 32, says she was unfairly ticketed for idling in front of a fire hydrant, according to court papers.

Diaz went to pick up a pizza in her brand new BMW last November, but police took exception to her sitting in the still-running car.

She claims cops ticketed her for parking at the hydrant, “obviously ignor[ing] the basic rules of parking in NYC (i.e. there is a difference between parking in front of a fire hydrant and merely idling in front of said hydrant).”

City traffic rules make clear it’s OK to idle a car in front of a hydrant, as long as the driver is ready to move it. The city said it will review the suit.